Hindawi Publishing Corporation
Neuroscience Journal
Volume 2013, Article ID 304674, 11 pages
http://dx.doi.org/10.1155/2013/304674
Research Article
Cognitive, Affective, and Motivational Changes
during Ostracism: An ERP, EMG, and EEG Study
Using a Computerized Cyberball Task
Taishi Kawamoto,1,2 Hiroshi Nittono,1 and Mitsuhiro Ura3
1
Graduate School of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashihiroshima 739-8521, Japan
Japan Society for the Promotion of Science, 5-3-1 Kojimachi, Chiyoda 102-0083, Japan
3
Department of Psychology, Otemon Gakuin University, 2-1-15 Nishiai, Ibaraki 567-8502, Japan
2
Correspondence should be addressed to Taishi Kawamoto; [email protected]
Received 6 July 2013; Revised 3 September 2013; Accepted 23 September 2013
Academic Editor: Stefan Berti
Copyright © 2013 Taishi Kawamoto et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Individuals are known to be highly sensitive to signs of ostracism, such as being ignored or excluded; however, the cognitive,
affective, and motivational processes underlying ostracism have remained unclear. We investigated temporal changes in these
psychological states resulting from being ostracized by a computer. Using event-related brain potentials (ERPs), the facial
electromyogram (EMG), and electroencephalogram (EEG), we focused on the P3b amplitude, corrugator supercilii activity,
and frontal EEG asymmetry, which reflect attention directed at stimuli, negative affect, and approach/withdrawal motivation,
respectively. Results of the P3b and corrugator supercilii activity replicated findings of previous studies on being ostracized by
humans. The mean amplitude of the P3b wave decreased, and facial EMG activity increased over time. In addition, frontal EEG
asymmetry changed from relative left frontal activation, suggestive of approach motivation, to relative right frontal activation,
indicative of withdrawal motivation. These findings suggest that ostracism by a computer-generated opponent is an aversive
experience that in time changes the psychological status of ostracized people, similar to ostracism by human. Our findings also
imply that frontal EEG asymmetry is a useful index for investigating ostracism. Results of this study suggest that ostracism has well
developed neurobiological foundations.
1. Introduction
People are sensitive to social exclusion. Sometimes, a slight
social rejection evokes emotional pain in excluded individuals [1–7]. According to an evolutionary perspective, sensitivity to social exclusion is necessary for human survival [4, 8],
because social isolation is often a fatal threat [9, 10]. Therefore,
humans have developed monitoring systems that are highly
sensitive to cues indicative of social exclusion [11, 12].
It is known that people can detect the slightest cue indicative of ostracism and as a result develop aversive feelings. Laboratory studies have demonstrated that ostracism during a
computerized ball-tossing game called Cyberball triggers
negative affect and lowers the degree to which individuals are
able to fulfill their four fundamental needs: belonging, control, self-esteem, and meaningful existence [4]. This effect was
observed even when participants knew that the ostracizing
others were computer-generated players or when they knew
beforehand that they would be ostracized [7]. Functional
magnetic resonance imaging (fMRI) studies have shown that
social exclusion provokes social pain, which is reflected in
activation of the dorsal anterior cingulate cortex (dACC) [1].
Since this region is also associated with physical pain [13, 14],
it has been proposed that social and physical pain share a
common neural alarm system [15]. These findings suggest
that people are sensitive to being accepted or excluded by
others, and that their emotional reactivity to these social situations can be mapped onto specific neural circuitry.
2
Despite extensive research on ostracism, relatively few
studies have focused on the time course of changes in psychological states during such situations. Instead, prior research
has focused primarily on postexclusion feelings or experiences of overall social exclusion. It is important to understand
the temporal dynamics of psychological states underlying
ostracism, because reactions to ostracism are considered to be
dynamic processes [16], such that ostracism is associated with
specific emotional states and cognitive efforts to reappraise
the situation [1, 4]. In their pioneering work, Themanson et al.
demonstrated that attention to exclusionary cues decreased
with time [17]. These results were also corroborated by an
fMRI study [18]. In addition, a behavioral study using a selfreport measure has revealed that negative affect in response to
ostracism increased with time [19]. Other studies have investigated neural and psychophysiological mechanisms that are
closely related to appraisal and regulation of aversive impact
of ostracism [20–22]. However, it is unclear whether temporal
changes in psychological status also occur in response to
ostracism by a computer-generated opponent. In addition,
relatively few studies have included multiple psychophysiological measures in one study design. In the present study, we
used physiological measurements and investigated the time
course of cognitive, affective, and motivational processes that
are associated with ostracism by computer-generated opponents.
It is known that social exclusion is one of the causes
of psychological problems including depression [23] and
aggression, as has been reported in cases of school shootings
[24]. Therefore, it is important to understand ostracism in
more detail, in order to develop countermeasures against the
psychological difficulties that it causes. It is known that using
a computer-generated opponent can enhance experimental
validity, because computers are the perfect research confederates [25]. Thus, it is valuable for future research to clarify
whether ostracism by a computer or a computer-generated
opponent can also cause aversive feelings and psychological
changes similar to ostracism by humans. Based on the studies
suggesting that people respond to humans and computers in
a similar manner [25, 26] and that ostracism from computergenerated opponents evokes social pain [3], we predicted that
ostracism by computer-generated opponents would evoke
subjective and neurobiological responses similar to ostracism
by human.
To investigate cognitive processes, we measured eventrelated potentials (ERPs). Among the various ERP indices, we
focused on the P3b component, because this component has
been extensively studied in relation to cognitive processing
under unpredictable situations and also because it has been
the focus of social exclusion studies. The P3b component has
been associated with multiple cognitive functions, including
attentional allocation and task-relevance evaluation [27]. This
component is elicited by a task-relevant event and shows
a larger amplitude for a more significant event [28, 29] or
for events with a lower subjective probability [30, 31]. The
amplitude of the P3b component is generally interpreted as an
index of attention directed at eliciting stimuli [30, 32, 33]. A
previous study has indicated that P3b amplitude in response
to exclusionary cues is associated with self-reported need
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threat and that this amplitude decreased with time [24].
Therefore, we predicted that P3b amplitude would be larger
during the initial phase of an interaction and that this amplitude would be associated with self-rated social pain.
Facial electromyogram (EMG) activity was utilized to
investigate affective processes. Facial EMG activity over the
corrugator supercilii, which is located above the eyebrows,
is inversely related to the valence of a subjective experience.
In general, pleasant stimuli elicit less activity and unpleasant
stimuli elicit more activity than neutral stimuli [34]. Since this
activity has been a reliable measure of negative affect [35, 36],
the negative affect induced by social exclusion should be
reflected by increased facial EMG activity over the corrugator
supercilii. A previous study has reported that negative affect
increased with time [19]. Therefore, we predicted that facial
EMG activity would increase with time during social exclusion.
Electroencephalogram (EEG) was utilized in order to
investigate the motivational processes associated with social
exclusion. It has been demonstrated that asymmetrical activity in the frontal lobes within the alpha band (i.e., alpha
power) is related to motivation and/or emotional factors.
Alpha power is inversely related to cortical activation [37].
Previous research has demonstrated that activation of the left
frontal cortex is associated with approach-related motivation,
whereas that of the right frontal cortex is associated with
withdrawal-related motivation [38–41]. In terms of the alpha
asymmetry index (i.e., ln[right alpha power] − ln[left alpha
power]), a positive score reflects higher right frontal alpha
power (i.e., relative left frontal activity) and a negative score
reflects higher left frontal alpha power (i.e., relative right
frontal activity). Given the previous finding indicating that
P3b amplitude and dACC activation in response to exclusion
cues decreased with time [17, 18], ostracized people may consider shifting the motivational direction to effectively cope
with ostracism. Since participants cannot interact with others
during ostracism, we predicted that relative right frontal
activity (i.e., withdrawal motivation) would be observed in
the later phase of an interaction.
In the present study, participants were asked to play a simple ball-tossing game called Cyberball [5] with two computergenerated opponents [7]. In addition to the exclusion condition, we set up two comparison conditions: a fair play
condition, which has been used as a control condition in prior
research [1, 2, 5, 7], and an observation condition, designed to
compare the variation of temporal changes in psychological
states across conditions. In the observation condition, participants observed the players tossing the ball to each other. The
exclusion condition was similar to the observation condition,
with the exception that the participant becomes aware that
the ball is not being tossed to him or her. The observation condition was used to control (1) the probability that the ball does
not come to the participant and (2) participant’s responses
when he or she needed to throw the ball to the other players.
In the fair play condition, participants joined in the game
equally with the other two players. To examine the time
course of cognitive, affective, and motivational processes during exclusion, the first and second halves of the observation,
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exclusion, and fair play conditions were analyzed separately,
similar to previous studies [17, 18].
We tested three hypotheses in the present study. First, P3b
amplitude during the exclusion condition would be larger in
the initial phase of an interaction (i.e., first half) than in the
later phase of an interaction (i.e., second half). Second, corrugator supercilii activity during the exclusion condition would
be larger in the later phase of an interaction than in the initial
phase of an interaction. Finally, relative right frontal activity
(i.e., withdrawal motivation) would be observed in the later
phase of an interaction relative to the initial phase of an interaction during the exclusion condition.
2. Materials and Method
2.1. Participants. Healthy undergraduates (𝑁 = 19, 11 women
and 𝑀age = 18.3 years) attending Hiroshima University, in
Higashi-Hiroshima city, Japan, participated in the experiment. All participants were right handed, as assessed by
the Edinburgh Handedness Inventory [42]. Research Ethics
Committee of the Graduate School of Integrated Arts and Science, Hiroshima University, approved the research protocol.
All participants gave their written informed consent for participation in the study.
2.2. Design and Materials. The original Cyberball task [5] was
modified for the ERP to make the timing of the ball toss
clearer and more discernible. Participants were instructed to
practice their mental visualization skills during the game.
They were told that performance in the game was unimportant because the game was merely a means for them to engage
their mental visualization skills. Similar to a previous study
[7], participants in this study were also aware that other players did not actually exist.
Figure 1 shows a schematic diagram of the task. Two computer-generated opponents (blue and red squares) appeared
at the top right and the top left corners of the screen. The participant appeared as a green square with the word “YOU” at
the bottom of the screen. To predict the timing of the ball toss
more precisely, the ball (a single circle) was programmed to
change to a double circle 1500 ms before being tossed. The ball
traveled for 1000 ms until another player received it. Participants used their left and right index fingers placed on a
response pad to toss the ball to the player on their right or
left.
The Cyberball task was used in all three conditions.
Although the primary interest was in the last, exclusion condition, the typical procedure used in previous studies (i.e., the
order of conditions) was followed [1, 43, 44]. First, participants were asked to observe the other two computer-generated opponents tossing the ball to each other (observation
condition), which lasted for 45 trials (approximately 150
seconds). Then, participants joined in the game with the other
two computer-generated opponents (fair play condition).
This fair play condition consisted of three blocks, each consisting of 45 trials (approximately 150 seconds) as to control
the length of the time across the condition. During fair play,
3
ERP recordings
−200 ms 800 ms
1000–2000 ms
YOU
1500 ms
1000 ms
YOU
YOU
YOU
YOU
YOU
Figure 1: A schematic diagram of the modified Cyberball task used
in the present study. The ball (a single circle) was changed to a double
circle 1500 ms before tossing. Then, the ball moved to the participant
or to the other player. The computer players held the ball for a
random period lasting between 1000 and 2000 ms. When the ball
appeared, the participant selected to toss it to the left or right player
by pressing one of two buttons. ERPs were recorded time locked to
the ball toss of the computer players.
computer-generated opponents threw to each other 45 times
(not receiving the ball) and threw to the participant 45 times
(inclusion). The participant threw back to the computergenerated opponents the remaining 45 times. After these two
conditions, the participants unknowingly completed a block
in which the other computer-generated opponents suddenly
excluded the participant (exclusion condition). In this block,
the ball was tossed to the participant only once on the first
trial and was not tossed to the participant during the subsequent 45 trials (approximately 150 seconds).
During short breaks between the blocks, participants
completed a questionnaire that assessed social pain [7, 45–
47]. Social pain was measured using four statements designed
to assess the participants’ subjective experiences (e.g., “I felt
liked,” “I felt rejected,” “I felt invisible,” and “I felt powerful”).
These experiences were rated on a 9-point scale ranging from
1 (Not At All) and 9 (Very Much). Two items, “I felt liked” and
“I felt powerful,” were reverse scored such that higher scores
for each item indicated a greater level of social pain. The
average value of the four items was used as a social pain index.
2.3. Physiological Measurement, Recordings, and Processing.
The EEG was recorded at 39 scalp sites (Fp1/2, AFz, Fz, F3/4,
F7/8, FCz, FC1/2, FC5/6, FT9/10, Cz, C3/4, T7/8, CPz, CP1/2,
CP5/6, TP9/10, Pz, P3/4, P7/8, POz, PO9/10, Oz, O1/2, and
Iz) using Ag/AgCl electrodes on an elastic cap (EASYCAP
GmbH, Germany). Vertical and horizontal electrooculograms were recorded from electrodes attached above and
below the left eye and at the outer canthi. Electrode impedances were less than 5 KΩ. The signal was recorded with a
bandpass filter of 0.016–120 Hz at a sampling rate of 500 Hz
using a digital EEG amplifier (Nihon-Kohden, EEG1100). The
data were rereferenced to the linked earlobes offline. A digital
bandpass filter of 0.1–60 Hz and 0.1–100 Hz was applied for
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9
8
7
6
Social pain
the ERP and EEG, respectively. Ocular artifacts were corrected using the method of Gratton et al. [48] implemented
in Brain Vision Analyzer 1.05 (Brain Products, Germany). In
our design, the fair play condition differed from the other two
conditions with regard to participants’ response (i.e., throw
to other players) and direction of the ball (i.e., receiving the
ball from other players). To prelude the influence of these
differences, ERP results were analyzed only for trials in which
participants did not receive the ball during observation, fair
play, and exclusion conditions. ERP waveforms were obtained
by averaging a 1000 ms period between 200 ms before and
800 ms after the stimulus onset (i.e., the period of the ball
movement) separately for the first half (i.e., the first 20 trials
where the ball did not come to the participant) of the block for
observation and exclusion conditions. Because fair play was
conducted for three blocks, the first half contains the first 7
trials where the ball did not come to the participant across
blocks (i.e., 21 trials) and the second half contains the last 7
trials where the ball did not come to the participant across
blocks (i.e., 21 trials). After visual inspection, trials that
contained nonocular artifacts were excluded from averaging.
Artifact-free trials were then averaged (𝑀 = 18.66, SD =
1.90, range: 12 to 21 trials). The amplitude of P3b was measured at Pz as the mean amplitude that was observed 350 to
450 ms after stimulus onset, based on the ranges used in previous studies [17, 22] and visual inspection of the grand mean
waveforms in the present study.
An EMG over the corrugator supercilii was recorded
using a pair of miniature electrodes above the left eye, according to the recommendation of Fridlund and Cacioppo [49].
Electrode impedances were less than 5 KΩ. The sampling rate
was 500 Hz. The raw EMG signal was filtered with a high-pass
filter of 90 Hz and rectified [50]. Each block was subdivided
into 15 temporal segments (10 sec each: 𝑇1 –𝑇15 ) and the mean
EMG amplitude in each segment was calculated. Any segment with an amplitude value exceeding the mean ± 3 standard deviations of each participant was regarded as an outlier
and linearly interpolated using the values of the former and
subsequent segments (this involved less than 5% of the segments). Then, the change of EMG activity from the beginning
(𝑇1 ) was calculated (variation index: Log 𝑇𝑛 − Log 𝑇1 , where 𝑛
was segment number (1 to 15)). To investigate temporal
changes similar to ERP, the mean EMG activity was calculated
separately for the first half (i.e., average from 𝑇2 to 𝑇8 ) and
for the second half (i.e., average from 𝑇9 to 𝑇15 ) of the block.
Because fair play was conducted in three blocks, average
activity (i.e., first and second halves) of the three blocks was
used as EMG activity during fair play. To check the difference
across fair play blocks, we conducted a 3 (block: first fair
play block versus second fair play block versus last fair play
block) × 2 (segment: first half versus second half) ANOVA,
but there was no statistically significant main effect of block
and interaction between block and segment (𝐹(1, 18) = 0.46,
𝑃 = 0.66, 𝐹(2, 36) = 1.37, 𝑃 = 0.27, resp.).
Alpha power from lateral frontal sites (𝐹7, 𝐹8) was calculated by fast Fourier transform using a Hamming window
within the alpha band (8–13 Hz) separately for the first half
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4
3
2
1
Observation
Fair play
Exclusion
Figure 2: Subjective social pain scores for observation, fair play,
and exclusion conditions. Higher scores indicate higher social pain.
Error bars indicate the standard error of means across participants.
(i.e., the first 70 seconds) and the second half (i.e., the last
70 seconds). Asymmetry scores were then calculated by subtracting the natural log of alpha power from the left electrode
(𝐹7) from the corresponding electrode over the right hemisphere (𝐹8). Because fair play was conducted in three blocks,
average activity (i.e., first and second halves) of the three
blocks was used as an asymmetric index during fair play. To
assess the difference across fair play blocks, we conducted a 3
(block: first fair play block versus second fair play block versus
last fair play block) × 2 (segment: first half versus second
half) ANOVA, but there was no statistically significant main
effect of block and interaction between block and segment
(𝐹(1, 18) = 1.68, 𝑃 = 0.21, 𝐹(2, 36) = 1.28, 𝑃 = 0.29, resp.).
Since alpha power is inversely related to cortical activity,
higher alpha power on the left side relative to the right side
indicates greater activity in the right than the left [37].
3. Results
3.1. Subjective Ratings. As seen in Figure 2, the mean social
pain ratings were 5.41, 3.46, and 6.71 for the observation,
fair play, and exclusion conditions, respectively. To check the
effectiveness of the manipulation, a one-way repeated measures analysis of variance (ANOVA) was conducted on the
social pain ratings. There was a significant main effect of condition (𝐹(2, 36) = 57.37, 𝑃 < 0.05, 𝜂𝑝2 = 0.76). Post hoc comparisons using paired 𝑡-tests with Bonferroni corrections
showed that these means all differed significantly from each
other (𝑃s < 0.05). These results confirmed that social pain
was effectively elicited during the exclusion condition.
3.2. ERP. Figure 3 shows the grand mean ERP waveforms
in the observation and exclusion conditions (left side) and
the mean P3b amplitudes in the first and second halves of
the exclusion and observation conditions at Pz (right side).
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−5 𝜇V
12
10
800 ms
Pz
P3 amplirude (𝜇V)
−200
8
6
4
2
0
15
Observation
Observation
Fair play
Exclusion
Fair play
Exclusion
First half
Second half
(a)
First half
Second half
−10
10
Observation
Fair play
Exclusion
(𝜇V)
(b)
Figure 3: Results of ERP. (a) Grand mean ERP waveforms at Pz elicited by ball tosses to the other player during observation, fair play, and
exclusion (left side) and P3b amplitudes (350–450 ms) in the first half and second half of blocks in each condition (right side). Error bars
indicate standard errors of means across participants. (b) Topographical map of the first and second half of blocks in each condition.
A 3 (condition: observation versus fair play versus exclusion)
× 2 (segment: first half versus second half) ANOVA showed a
significant main effect for condition (𝐹(2, 36) = 30.04, 𝑃 <
0.05, 𝜂𝑝2 = 0.63) and segment (𝐹(1, 18) = 27.36, 𝑃 < 0.05,
𝜂𝑝2 = 0.60). The interaction between condition and segment
was also statistically significant (𝐹(1, 36) = 10.79, 𝑃 < 0.05,
𝜂𝑝2 = 0.36). Post hoc analysis revealed that P3b amplitude
during the exclusion and fair play conditions was larger for
the first half block than for the second half block (𝑃s < 0.05),
although this difference was not statistically significant during the observation condition (𝑃 = 0.97). In addition, these
means for the first and second half blocks were larger during
fair play condition than during observation and exclusion
conditions (𝑃s < 0.05). Furthermore, P3b amplitude for the
first half block was larger during exclusion condition than
6
3.3. EMG. Figure 5 shows the mean time course of facial
EMG (i.e., corrugator supercilii) activity within a block of
each condition (left side) and in the first and second halves of
the observation, fair play, and exclusion blocks (right side). A
3 (condition: observation versus fair play versus exclusion) ×
2 (segment: first half versus second half) ANOVA showed a
statistically significant main effect of condition (𝐹(1, 36) =
4.48, 𝑃 < 0.05, 𝜂𝑝2 = 0.20) and segment (𝐹(1, 18) = 16.61, 𝑃 <
0.05, 𝜂𝑝2 = 0.48). The interaction between condition and segment was also statistically significant (𝐹(1, 36) = 6.93, 𝑃 <
0.05, 𝜂𝑝2 = 0.28). Post hoc analyses revealed that facial EMG
activity for the second half block was larger during the exclusion condition than during the observation (𝑃 < 0.05) and
fair play conditions (𝑃 = 0.07), while these differences were
not statistically significant for the first half block (𝑃s > 0.25).
In addition, corrugator supercilii activity in the second half
block was significantly larger than in the first half block for all
conditions (𝑃s < 0.05).
To examine the relationship between facial EMG activities and subjective ratings during exclusion, Pearson’s correlation coefficients were computed. Facial EMG activity during
the first half of the exclusion block was weakly correlated with
social pain (𝑟(17) = 0.42, 𝑃 = 0.08). In contrast, both facial
EMG activities during the second half exclusion block and the
difference value were not statistically significantly related to
social pain (𝑟s < 0.38, 𝑃s > 0.11).
3.4. Frontal EEG Asymmetry. Figure 6 shows the mean asymmetry scores for the first and second halves of the observation, fair play, and exclusion conditions. A 3 (condition:
observation versus fair play versus exclusion) × 2 (segment:
first half versus second half) ANOVA showed a marginally
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8
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Social pain ratings (1–9)
during observation condition (𝑃 < 0.05), while this difference was not significant in the second half block (n.s.).
To examine the changes in P3b amplitude, a one-way
repeated ANOVA was performed on the difference value. The
difference value was calculated by subtracting P3b amplitude
in the first half block from that in the second half block.
There was a statistically significant main effect of condition
(𝐹(2, 36) = 10.79, 𝑃 < 0.05, 𝜂𝑝2 = 0.36). Post hoc comparisons
showed that the difference value was more negative during
the exclusion condition than during the observation and fair
play conditions (𝑃s < 0.05). There was no statistically significant difference between observation and fair play conditions
(𝑃 = 0.61).
To examine the relationship between P3b amplitude
and subjective ratings during exclusion, Pearson’s correlation
coefficients were computed. P3b amplitude during the first
half exclusion block was positively correlated with social pain
(𝑟(17) = 0.53, 𝑃 < 0.05; see Figure 4), whereas P3b amplitude
during the second half exclusion block was not statistically
significantly related to social pain (𝑟(17) = 0.15, 𝑃 = 0.40). In
addition, there was a weak correlation between the difference
value and social pain (𝑟(17) = −0.45, 𝑃 = 0.06). However, the
relationship between the difference value and social pain was
not statistically significant after controlling the P3b amplitude
during the first half block (𝑟(17) = −0.07, 𝑃 = 0.77).
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5
4
3
r = 0.53, P = 0.020
2
1
−5
0
5
10
15
20
P3 amplitude for the first half
Figure 4: Scatter plots of P3b amplitude and self-rated social pain
scores during social exclusion. 𝑋-axis indicates P3b amplitude for
the first half of blocks during social exclusion.
significant main effect of condition (𝐹(1, 36) = 2.46, 𝑃 = 0.10,
𝜂𝑝2 = 0.12). The interaction between condition and segment
was statistically significant (𝐹(1, 36) = 8.04, 𝑃 < 0.05, 𝜂𝑝2 =
0.31). Post hoc analyses revealed that the asymmetry index
for the second half block was more negative during the exclusion than during the observation and fair play conditions
(𝑃s < 0.05), while these differences were not statistically
significant for the first half block (n.s.). In addition, the asymmetry score during the exclusion condition was significantly
more negative for the second half block than for the first half
block (𝑃 < 0.05), while this difference was not statistically
significant during observation and fair play conditions (𝑃s >
0.16).
To examine the relationship between asymmetry score
and subjective ratings during exclusion, Pearson’s correlation
coefficients were computed. No statistically significant relationships were found.
4. Discussion
We investigated the time course of cognitive (i.e., P3b amplitude), affective (i.e., facial EMG activity), and motivational
processes (i.e., frontal EEG asymmetry indexes) while being
ostracized by a computer-generated opponent, by using
a modification of the Cyberball task. We simultaneously
recorded ERPs elicited by exclusion cues, facial EMG activity
over the corrugator supercilii, and frontal EEG activities.
Consistent with the predictions of the study, P3b amplitude
during the exclusion condition was larger in the first half,
relative to the second half of the task. In addition, corrugator
supercilii activity during social exclusion was larger in the
second half than in the first half of the task. Furthermore, during the exclusion condition, we observed relatively stronger
Facial EMG activity (𝜇V)
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0.8
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
0
T1
T5
T10
T15
Observation
Fair play
Exclusion
Segment
First half
Observation
Fair play
Exclusion
Second half
(a)
(b)
Figure 5: The results of EMG. Time course of EMG activity over the corrugator supercilii during the observation, fair play, and exclusion
conditions (a) and the mean EMG activities aggregated in the first half and second half of blocks in each condition (b). Error bars indicate
the standard error of means across participants.
left frontal activity (i.e., approach motivation) in the first half
of the task, whereas relatively stronger right frontal activity
(i.e., withdrawal motivation) was observed in the second half
of the task. Such changes were not detected or were only
weekly observed in the observation and fair play conditions
in which there was no ostracism. These findings suggest
that cognitive, affective, and motivational processes resulting
from being ostracized by a computer-generated opponent
were similar to changes resulting from being ostracized by
humans [17–19].
Participants felt more social pain during the exclusion
condition, as has been reported in previous studies [1, 4].
In other words, participants felt social pain, even without
conducting higher-order processing to conduct the excluders’
mental state, or intention. This finding implies that social pain
can be caused by superficial cues such as the frequency of ball
throws. Because ostracism causes various psychological problems [23, 24], people have a detection system that is highly
sensitive to ostracism [11, 12]. Our findings strongly suggest
that people can detect the slightest cue of ostracism and as a
result experience aversive feelings. This idea was also confirmed by the result of the observation condition; although
social pain was lower during observation than exclusion, participants felt some social pain in the observation condition
compared to the inclusion condition.
Patterns of physiological measurements and self-rated
items identified cognitive and affective processes underlying
ostracism. First, attention to exclusion cues decreased with
time, as was indicated in a previous study [17]. It is possible
that the first experience of being excluded elicits strong aversive responses associated with violated expectations of fair
play and detection of social exclusion. These may decline after
multiple rejections. In line with this idea, previous research
has shown that during social exclusion, dACC activity, which
serves to detect social exclusion and for social pain appraisal
[1, 47], was larger in the initial phase of an interaction than in
the later phase of an interaction [18]. Such findings suggest
that once an individual detects social exclusion, he or she
moves attention away from exclusion cues. In the present
study, the P3b amplitude in the first half of the task during
the exclusion condition was strongly and positively correlated
with subjective social pain. This finding is consistent with the
notion that social pain triggers an individual’s attention to
focus on the source of an exclusion, so as to determine if the
exclusion is potentially threatening or important [4]. Our
findings suggest that greater attention to exclusion cues in the
initial phase of an interaction increases immediate social
pain.
Interestingly, we also found that P3b amplitude in the second half of the block did not differ between the observation
and exclusion conditions; attentional allocation to the exclusionary cues seems to be similar in both conditions at the
later stage of the interaction. This finding raises some possible
alternative interpretations regarding the results of P3b. The
Cyberball task includes multiple factors related to the participants, which change over time. These include subjective
8
Neuroscience Journal
0.15
The asymmetry indexes
0.1
0.05
0
−0.05
−0.1
−0.15
Observation
Fair play
Exclusion
First half
Second half
Figure 6: Frontal asymmetry indexes for the first and second halves
in each condition. Positive score indicates approach motivation,
whereas negative score indicates withdrawal motivation. Error bars
indicate the standard error of means across participants.
probability and personal significance of events and such
factors may also affect P3b amplitude [28–33]. Thus, in the
later stage of the interaction during ostracism, participants
might have noticed that they would never receive the ball.
Accordingly, the results of P3b can be interpreted not only
by merely ostracism-specific responses, but also task-relevant factors such as self-relevance or stimulus probability.
Exactly which factors—subjective social pain or stimulus
probability—reflect the processing of ostracism is a matter of
debate [15, 47, 51]. Ostracism is a complicated phenomenon
that inherently involves lower subjective probability and selfrelevance. Therefore, it is difficult to break ostracism into
distinct components. Nevertheless, it would be valuable for
future research to investigate whether the decline in the
P3b amplitude reflects merely ostracism-specific response or
other factors.
Second, results indicated that negative affect increased
with time, which was also consistent with a previous study
[19]. It should be noted that all conditions tended to increase
facial EMG activities over time. This was possibly due to
mental fatigue, which was involved in all the conditions [52].
What is more important, however, is that facial EMG activity
increased dramatically in the exclusion condition as compared to the other conditions. Findings of this study regarding
the P3b suggest that negative affect may be evoked even after
attention to exclusion cues has moved away from such cues
indicating that negative affect induced by exclusion was not
determined only by exclusion cues, but by the exclusion situation as a whole. Although our facial EEG data showed that
negative affect increased over time, previous findings suggest
that negative affect evoked by ostracism quickly recovers [19,
53]. Thus, it could be the case that negative affect accumulates
over time and decreases at a certain point. By taking previous
findings and our results into consideration, it would be possible to conclude that there is a time lag between negative affects
induced by ostracism and cognitive efforts to regulate these
negative affects. However, the issue of whether negative
affects recover over time and how they recover remains
unknown. It is suggested that future studies may benefit from
investigating the recovery process from negative affect during
ostracism, by manipulating the length of ostracism and by
focusing on individual differences.
The changes in frontal EEG found in this study are to the
best of our knowledge the first evidence of temporal changes
in frontal EEG during ostracism. This finding may suggest
that the direction of motivation shifted from an approach
state to a withdrawal state [38–42] because of ostracism. It is
known that ostracism is a deeply aversive event, and therefore, once individuals detect that they are being socially
excluded, they may feel, think, and behave so as to reestablish
the optimal level of their fundamental need to belong [4]. In
ostracism studies using Cyberball, participants do not have
an opportunity to interact with others during social exclusion, because the other players do not exist in the same room.
In this situation, because participants cannot engage with the
simulated other players, they cannot reestablish the optimal
levels of fundamental needs through the responses of other
players. Our findings imply that the shift in motivation to
a withdrawal state during the exclusion condition reflects
withdrawal from the situation of social exclusion and/or emotional withdrawal. In support of this idea, findings of this and
previous studies have indicated that attention and dACC
activation to exclusion cues decrease over time [17, 18]. Since
social exclusion is an aversive experience, individuals withdraw from exclusionary situations or screen themselves from
the negative effects of social exclusion. In corroborating this
possibility, previous studies have indicated that ostracized
people can quickly ameliorate the negative effect of ostracism
[19, 53], suggesting that people can effectively regulate the
negative effects of ostracism. The link between the asymmetry
observed during ostracism and withdrawal-related motivation and relationship between withdrawal-related motivation
and the processes of ameliorating the effects of ostracism
should be examined in future studies. Such investigations
would help fill the gap in knowledge resulting from the highly
limited number of investigations on ostracism using frontal
EEG [22, 54].
Although the observation and exclusion conditions
evoked social pain compared to the inclusion condition, the
time course of psychophysiological activities was considerably different. This finding is in line with previous studies
indicating that implicit social exclusion, such as when people
could not participate in a Cyberball task due to an Internet
malfunction, also evoked social pain; however that direct regulation of social pain did not occur in these cases [1, 43, 44].
Our findings also provided evidence that an ostracism-like
event—the observation condition—did not change psychological status. One possible reason for this could be that
people in the observation condition did not need to change
Neuroscience Journal
their psychological status, because they knew beforehand
not that they should join the task. That is, they could easily
change the meaning of ostracism before the task. Despite this,
an ostracism-like event—the observation condition—still
evoked social pain, which supports the notion that even the
slightest hint of ostracism evokes social pain [1–7]. More
research is needed to investigate the types of ostracism events
that cause direct regulation processes and psychological
changes, by focusing on the intensity and awareness about
ostracism.
There were several limitations to this study. First, similar
to prior research [1, 43, 44], the presentation order of our conditions was always identical (observation, fair play, and exclusion). It is possible that order and sequence effects may have
affected our results. Previous studies on ostracism have suggested that mere order effects do not cause the subjective and
neurobiological responses, such as social pain or dACC activity, in response to social exclusion [47]. Nevertheless, it is suggested that future studies should address this issue by implementing the task condition as a between-subjects factor or by
randomizing the order of the conditions. Second, we measured social pain in short breaks between blocks. It is possible
that social pain rating may affect the cover story and participants’ perception of ostracism. In some studies measured
social pain was given after all experimental conditions were
completed [1, 45–47], whereas other studies have measured
it immediately after each condition [43, 44]. In addition,
the fact that we observed ostracism-related psychological
changes and increases in subjective social pain suggests that
our design was adequate to produce the phenomena of interest. Nevertheless, future research is required to investigate
whether the frequency of social pain rating affects the meaning of ostracism. Third, although neither the exclusion, nor
the observation condition involved motor responses, the fair
play condition did involve a button-press response to throw
the ball. Previous studies have implied that P3b was affected
by motor preparation and motor responses [55–57]. Therefore, ERP differences among the conditions might be partly
due to movement-related activities. Although the fair play
condition (i.e., natural social interactions) inherently involves
motor responses, further studies would be needed to control
the effects of motor preparation and motor response on ERPs
by using other paradigms or stimuli, such as the rejection
paradigm [51] and facial expression stimuli [58, 59]. Forth,
there are individual differences in response to ostracism.
For example, it is known that people that are low in selfesteem have higher self-reported social pain, because they
hyperactivate the appraisal process (e.g., dACC) in response
to ostracism [46]. On the other hand, people high in
general trust are known to effectively regulate social pain
[43]. In addition, individual differences and neurobiological
responses to ostracism may interact to predict postrejection
aggression [60]. Thus, future studies would benefit from
investigating how individual differences modulate changes in
the psychological status during ostracism. Finally, the present
sample size was relatively small. Further studies should rectify
this shortcoming by investigating a larger sample to see if the
results of our study would be replicated.
9
5. Conclusion
We have provided evidence that ostracism by computergenerated opponents is an aversive experience and that psychological condition during ostracism changes over time.
More specifically we found that as a result of ostracism, attention to exclusion cues decreased with time, whereas negative
affect increased with time and motivation shifted to a withdrawal pattern. The present findings suggest that ostracism
has well developed neurobiological foundations.
Acknowledgments
This work was supported by a Grant-in-Aid for JSPS Fellows
(12J05780) from the Japan Society for Promotion of Science
to the first author. This work was also supported by a Grantin-Aid for Scientific Research (B) 23330196 from the Japan
Society for Promotion of Science to the last author.
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